If you haven’t noticed, gardens are popping up in some unconventional places – from prison yards to retirement and veteran homes to programs for troubled youth.

Most are handy sources of fresh and local food, but increasingly they’re also an extension of therapy for people with mental health issues, such as post-traumatic stress disorder, or PTSD; depression; and anxiety.

It’s called horticultural therapy. And some doctors, psychologists and occupational therapists are now at work to test whether building, planting, and harvesting a garden can be a therapeutic process in its own right.